This application claims the priority of German Patent Application Serial No. 199 27 310.3, filed Jun. 15, 1999, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a working platform assembly, and more particularly to a working platform assembly of a type having a platform which can be extended and collapsed by means of a scissor-type mechanism having a lower pair of arm members which is connected with at least one upper pair of arm members positioned thereabove.
French Pat. No. FR 2 197 397 describes a working platform which is generally mounted on a truck or bogie and extended hydraulically at the job site to elevate persons or objects on the working platform to the required height.
Working platforms with relatively low working heights include two pairs of arm members, while those for high elevations may have five or more pairs of arm members to reach working heights in excess of 20 meters. Such high-elevation working platforms suffer, however, shortcomings because even in a collapsed state they may reach a maximum height permissible for road transport.
It would therefore be desirable and advantageous to provide an improved working platform assembly which obviates prior art shortcomings and exhibits a minimum height for transport, without adversely affecting the stability or load-carrying capability thereof.
According to one aspect of the present invention, a working platform assembly includes a platform and a scissor-type mechanism for extending and retracting the platform, with the scissor-type mechanism having a plurality of superimposed pairs of arm members, thereby defining a lower first pair of arm members and at least one further second pair of arm members being positioned thereabove, wherein the arm members of the first and second pairs of arm members have a cross section which decreases in upward direction, wherein the second pair of arm members has an upper end and includes an inner side formed with an outwardly directed slope which is realized by attaching the upper end of the arm members at a slanted angle.
The present invention resolves prior art problems by recognizing the fact that loads to be absorbed by the arm members decrease from bottom to top, so that the cross section of the arm members (profile height and wall thickness) can be decreased from bottom to top in accordance with the decreasing stress, thereby realizing a lower transport height of the working platform. Such a reduction in cross section in straight arm members is only possible to a limited extent because the offset between the inner and the corresponding outer arm members progressively increases towards the top, so that the use of bolts for implementing the hinged connection is no longer possible. By using slanted arm members in accordance with the present invention, this problem is eliminated.
As a consequence of the slanted configuration, the arm members can be collapsed to rest on one another, without formation of spaces in-between, thereby realizing a maximum operating height and a minimum transport height.
According to another feature of the present invention, the upper end of the arm members has a smaller cross section than the remaining portion of the arm members. As the upper end of the arm members has to absorb smaller forces than the remaining portion of the arm members, it is sufficient to configure the upper end portion with a smaller cross section.
According to another feature of the present invention, the slope increases from one pair of arm members to the pair of arm members positioned thereabove. In this way, the arm members rest safely in an optimum manner upon one another, when the working platform is collapsed.
According to another feature of the present invention, the length of the slanted upper end of the arm members increases relative to the overall length of the arm members from one pair of arm members to the pair of arm members positioned thereabove. This configuration results in an even tighter disposition of the arm members upon one another, when the working platform is collapsed.
In accordance with the present invention, even when the cross section of the arm members decreases from bottom to top, the arm members can rest on one another, without any space in-between, when the working platform is collapsed, whereby the decrease in cross section of the arm members can be randomly selected or staggered. The offset disposition, as encountered in conjunction with conventional straight designs of arm members is compensated by the slanted configuration of the arm members in accordance with the present invention. As a consequence, the transport height of the platform assembly and the weight of the scissor-type mechanism are reduced, while at the same time realizing a higher working height at same transport characteristics.